This invention pertains to the art of lighting systems and more particularly to lighting systems employing a receptive component such as a light guide etc. The invention is particularly applicable to arrangements requiring an increase in brightness in the light guide and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in other environments and applications. For example, the arrangement can also be used where a backup, or redundant, light source is required. Still another use of the lighting system finds application where two distinct levels of light brightness are required. Examples of different applications requiring high brightness include automotive headlight projection systems and LCD TV projection systems. These systems utilize a lens rather than a light guide as a light receptive component.
Recent developments confirm an increased emphasis and trend to use light guides or light conductors in various lighting systems. The benefits offered by such an arrangement, for example the ability to centralize a single light source and provide light via the light guides to a number of remote locations, suggests that an increased emphasis in use of this technology is warranted.
A low wattage light source is preferred for the light source because of the an ever increasing demand for efficiency, but simultaneously a need still exists to increase the brightness level at the input end of the light guide. That is, brightness, which is defined as the number of lumens per unit area per unit solid angle, on the order of 5,000 lumens per centimeter squared or higher is desired for certain applications. For example, such a high brightness level is desired for use in an automotive headlamp.
Another competing goal from a practical standpoint is to minimize the size of the light guide. Thus, if the cross-sectional area of the light guide is minimized, a greater amount of light must be provided to the input end of the light guide in order to maintain a predetermined brightness for the lighting system. Stated another way, the amount of light carried by the light guide must be relatively large. One way this can be accomplished is by increasing the effective brightness of the light source and concentrating the light into a smaller cross-sectional area.
Yet another important feature desired by a designer for selected applications is to provide redundancy to the lighting system. Although redundancy is not a crucial factor in all lighting systems, in others it becomes highly critical and of major importance. For example, where a single, primary light source fails and the consequences of such failure are of great concern, a low cost and effective redundant arrangement is desired.
Still other lighting systems require periodic switching between two distinct light levels. One typical example is providing high and low beam in an automotive headlamp. It is contemplated that these brightness levels could be obtained in a number of different ways. According to a first arrangement, switching or regulating the light (i) at the light source, (ii) through the light guide, or (iii) at the output end of the light guide could be incorporated into the light guide assembly. Commonly assigned application Ser. No. 08/018,852 (LD 10094) U.S. Pat. No. 5,408,552 discloses various embodiments for switching between first and second light levels as desired for a particular end use. A second arrangement applicable here, and to be described in greater detail below, is to use multiple light sources to provide the distinct levels of light brightness. Accordingly, it has been deemed advantageous to provide a lighting system that effectively increases brightness to a light guide and offers the flexibility of alternative uses as described above.